U.S. patent number 9,337,499 [Application Number 14/098,904] was granted by the patent office on 2016-05-10 for dual electrolyte fuel cell assembly.
The grantee listed for this patent is Roger Ray Whitfield. Invention is credited to Roger Ray Whitfield.
United States Patent |
9,337,499 |
Whitfield |
May 10, 2016 |
Dual electrolyte fuel cell assembly
Abstract
A fuel cell assembly in which one or more dual cell modules is
created by "sandwiching" a first reactant chamber between two
electrolyte assemblies and enclosing the result within a
surrounding vessel containing the second reactant. Each dual cell
module thereby contains two operating electrolyte assemblies. In
such a configuration separate electrical conductors must be
provided to create the proper connections. In order to avoid the
resistance losses inherent in the use of edge connections, the
present invention preferably includes conductors that actually pass
through the electrolytes. These conductors are contained within an
assembly that electrically insulates the conductor where needed and
provides a gas-tight seal where needed.
Inventors: |
Whitfield; Roger Ray (St.
George Island, FL) |
Applicant: |
Name |
City |
State |
Country |
Type |
Whitfield; Roger Ray |
St. George Island |
FL |
US |
|
|
Family
ID: |
53272095 |
Appl.
No.: |
14/098,904 |
Filed: |
December 6, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20150162624 A1 |
Jun 11, 2015 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M
8/0204 (20130101); H01M 8/04089 (20130101); H01M
8/241 (20130101); H01M 8/0256 (20130101); H01M
8/2475 (20130101); H01M 8/1004 (20130101); H01M
8/2483 (20160201); H01M 8/0271 (20130101); Y02E
60/50 (20130101); H01M 2008/1293 (20130101); H01M
8/0228 (20130101) |
Current International
Class: |
H01M
8/04 (20160101); H01M 8/02 (20160101); H01M
8/10 (20160101); H01M 8/24 (20160101); H01M
8/12 (20160101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Fraser; Stewart
Assistant Examiner: Godo; Olatunji
Attorney, Agent or Firm: Horton; J. Wiley
Claims
Having described my invention, I claim:
1. A fuel cell for creating electricity by reacting a first
reactant and a second reactant, comprising: a. a first reactant
diffusion layer, containing said first reactant; b. a first
electrolyte assembly in fluid communication with said first
reactant in said first reactant diffusion layer, said first
electrolyte assembly containing a first anode, a first cathode, and
a first electrolyte; c. a second electrolyte assembly in fluid
communication with said first reactant in said first reactant
diffusion layer, said second electrolyte assembly containing a
second anode, a second cathode, and a second electrolyte; d. a
vessel containing said second reactant, said vessel surrounding and
completely enclosing said first reactant diffusion layer, said
first electrolyte assembly, and said second electrolyte assembly;
e. a first reactant inlet feeding said first reactant into said
first reactant diffusion layer; f. a second reactant inlet feeding
said second reactant into said vessel; g. a master anode; h. a
master cathode; and i. at least one electrical via passing through
said first electrolyte and connecting either said first anode to
said master anode or said first cathode to said master cathode.
2. A fuel cell for creating electricity as recited in claim 1,
wherein: a. said first reactant is hydrogen; b. said second
reactant is oxygen; and c. said at least one electrical via
connects said first anode to said master anode.
3. A fuel cell for creating electricity as recited in claim 1,
wherein: a. said first reactant is oxygen; b. said second reactant
is hydrogen; and c. said at least one electrical via connects said
first cathode to said master cathode.
4. A fuel cell for creating electricity as recited in claim 2,
further comprising a second electrical via passing through said
first electrolyte and connecting said first cathode to said second
anode.
5. A fuel cell for creating electricity as recited in claim 3,
further comprising a second electrical via passing through said
first electrolyte and connecting said first anode to said second
cathode.
6. A fuel cell for creating electricity as recited in claim 1,
further comprising: a. wherein said first reactant is hydrogen; b.
wherein said second reactant is oxygen; c. a second reactant
diffusion layer, containing said first reactant; d. a third
electrolyte assembly in fluid communication with said first
reactant in said second reactant diffusion layer, said third
electrolyte assembly containing a third anode, a third cathode, and
a third electrolyte; e. a fourth electrolyte assembly in fluid
communication with said first reactant in said second reactant
diffusion layer, said fourth electrolyte assembly containing a
fourth anode, a fourth cathode, and a fourth electrolyte; f. said
vessel surrounding said second reactant diffusion layer, said third
electrolyte assembly, and said fourth electrolyte assembly; e. a
third reactant inlet feeding said first reactant into said second
reactant diffusion layer; f. wherein said at least one electrical
via connects said first anode to said master anode; g. a second
electrical via passing through said first electrolyte and
connecting said first cathode to said second anode; h. a third
electrical via passing through said third electrolyte and
connecting said third anode to said second cathode; and i. a fourth
electrical via passing through said third electrolyte and
connecting said third cathode to said fourth anode.
7. A fuel cell for creating electricity as recited in claim 1,
further comprising: a. wherein said first reactant is oxygen; b.
wherein said second reactant is hydrogen; c. a second reactant
diffusion layer, containing said first reactant; d. a third
electrolyte assembly in fluid communication with said first
reactant in said second reactant diffusion layer, said third
electrolyte assembly containing a third anode, a third cathode, and
a third electrolyte; e. a fourth electrolyte assembly in fluid
communication with said first reactant in said second reactant
diffusion layer, said fourth electrolyte assembly containing a
fourth anode, a fourth cathode, and a fourth electrolyte; f. said
vessel surrounding said second reactant diffusion layer, said third
electrolyte assembly, and said fourth electrolyte assembly; e. a
third reactant inlet feeding said first reactant into said second
reactant diffusion layer; f. wherein said at least one electrical
via connects said first cathode to said master cathode; g. a second
electrical via passing through said first electrolyte and
connecting said first anode to said second cathode; h. a third
electrical via passing through said third electrolyte and
connecting said third cathode to said second anode; and i. a fourth
electrical via passing through said third electrolyte and
connecting said third anode to said fourth cathode.
8. A fuel cell for creating electricity as recited in claim 2,
further comprising a second electrical via passing through said
first electrolyte, wherein said second electrical via also connects
said first anode to said master anode.
9. A fuel cell for creating electricity as recited in claim 8,
further comprising a third electrical via passing through said
first electrolyte, wherein said third electrical via also connects
said first anode to said master anode.
10. A fuel cell for creating electricity as recited in claim 3,
further comprising a second electrical via passing through said
first electrolyte, wherein said second electrical via also connects
said first cathode to said master cathode.
11. A fuel cell for creating electricity by reacting a first
reactant and a second reactant, comprising: a. a first reactant
diffusion layer, containing said first reactant; b. a first
electrolyte assembly in fluid communication with said first
reactant in said first reactant diffusion layer, said first
electrolyte assembly containing a first anode, a first cathode, and
a first electrolyte; c. a second electrolyte assembly in fluid
communication with said first reactant in said first reactant
diffusion layer, said second electrolyte assembly containing a
second anode, a second cathode, and a second electrolyte; d. a
pressure-tight vessel containing said second reactant, said vessel
in fluid communication with said first electrolyte assembly and
said second electrolyte assembly and completely surrounding said
first electrolyte assembly and said second electrolyte assembly; e.
a first reactant inlet feeding said first reactant into said first
reactant diffusion layer; f. a second reactant inlet feeding said
second reactant into said vessel; g. a master anode; h. a master
cathode; i. at least one electrical via passing through said first
electrolyte and connecting either said first anode to said master
anode or said first cathode to said master cathode.
12. A fuel cell for creating electricity as recited in claim 11,
wherein: a. said first reactant is hydrogen; b. said second
reactant is oxygen; and c. said at least one electrical via
connects said first anode to said master anode.
13. A fuel cell for creating electricity as recited in claim 11,
wherein: a. said first reactant is oxygen; b. said second reactant
is hydrogen; and c. said at least one electrical via connects said
first cathode to said master cathode.
14. A fuel cell for creating electricity as recited in claim 12,
further comprising a second electrical via passing through said
first electrolyte and connecting said first cathode to said second
anode.
15. A fuel cell for creating electricity as recited in claim 13,
further comprising a second electrical via passing through said
first electrolyte and connecting said first anode to said second
cathode.
16. A fuel cell for creating electricity as recited in claim 11,
further comprising: a. wherein said first reactant is hydrogen; b.
wherein said second reactant is oxygen; c. a second reactant
diffusion layer, containing said first reactant; d. a third
electrolyte assembly in fluid communication with said first
reactant in said second reactant diffusion layer, said third
electrolyte assembly containing a third anode, a third cathode, and
a third electrolyte; e. a fourth electrolyte assembly in fluid
communication with said first reactant in said second reactant
diffusion layer, said fourth electrolyte assembly containing a
fourth anode, a fourth cathode, and a fourth electrolyte; f. said
vessel in fluid communication with said third electrolyte assembly
and said fourth electrolyte assembly; e. a third reactant inlet
feeding said first reactant into said second reactant diffusion
layer; f. wherein said at least one electrical via connects said
first anode to said master anode; g. a second electrical via
passing through said first electrolyte and connecting said first
cathode to said second anode; h. a third electrical via passing
through said third electrolyte and connecting said third anode to
said second cathode; and i. a fourth electrical via passing through
said third electrolyte and connecting said third cathode to said
fourth anode.
17. A fuel cell for creating electricity as recited in claim 11,
further comprising: a. wherein said first reactant is oxygen; b.
wherein said second reactant is hydrogen; c. a second reactant
diffusion layer, containing said first reactant; d. a third
electrolyte assembly in fluid communication with said first
reactant in said second reactant diffusion layer, said third
electrolyte assembly containing a third anode, a third cathode, and
a third electrolyte; e. a fourth electrolyte assembly in fluid
communication with said first reactant in said second reactant
diffusion layer, said fourth electrolyte assembly containing a
fourth anode, a fourth cathode, and a fourth electrolyte; f. said
vessel surrounding said second reactant diffusion layer, said third
electrolyte assembly, and said fourth electrolyte assembly; e. a
third reactant inlet feeding said first reactant into said second
reactant diffusion layer; f. wherein said at least one electrical
via connects said first cathode to said master cathode; g. a second
electrical via passing through said first electrolyte and
connecting said first anode to said second cathode; h. a third
electrical via passing through said third electrolyte and
connecting said third cathode to said second anode; and i. a fourth
electrical via passing through said third electrolyte and
connecting said third anode to said fourth cathode.
18. A fuel cell for creating electricity as recited in claim 12,
further comprising a second electrical via passing through said
first electrolyte, wherein said second electrical via also connects
said first anode to said master anode.
19. A fuel cell for creating electricity as recited in claim 18,
further comprising a third electrical via passing through said
first electrolyte, wherein said third electrical via also connects
said first anode to said master anode.
20. A fuel cell for creating electricity as recited in claim 13,
further comprising a second electrical via passing through said
first electrolyte, wherein said second electrical via also connects
said first cathode to said master cathode.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of fuel cells. More
specifically, the invention comprises a novel fuel cell
construction using two electrolytes per unit and internal
electrical connections rather than edge connections.
2. Description of the Related Art
Although the operation of a conventional fuel cell is well
understood by those skilled in the art, some explanation of the
terminology of the components and the operation of the assembly
will aid the reader's understanding. FIG. 1 shows a prior art fuel
cell assembly having only one cell. In general, a fuel cell
includes two reactants that are physically separated by some type
of electrolyte. There are many types of fuel cells, and they are
often categorized according to the type of electrolyte used. The
particular example shown in FIG. 1 uses a proton exchange membrane
("PEM") for electrolyte 14. It is commonly called a "PEM" fuel
cell.
The proton exchange membrane ("PEM") is flanked by a pair of porous
electrodes. Anode 12 is located on a first side of the PEM and
cathode 16 is located on the other side. A gas diffusion layer is
also located on each side of the PEM. Hydrogen diffusion layer 30
is located on the left side in the orientation of FIG. 1. Oxygen
diffusion layer 32 is located on the right side. Hydrogen inlet 18
feeds gaseous hydrogen into the hydrogen diffusion layer, while
oxygen inlet 20 feeds gaseous oxygen into the oxygen diffusion
layer. A "diffusion layer" may be created using many known
techniques. A diffusion layer is commonly created using a sealed
manifold containing the particular flowing reactant gas.
Negative charge collector 54 is in contact with hydrogen diffusion
layer 30 while positive charge collector 56 is in contact with
oxygen diffusion layer 32. External conductor path 22 electrically
connects the negative charge collector to the positive charge
collector. Electrical load 24 is placed in this conductor path. A
typical goal for the operation of such a fuel cell is the creation
of an electrical current in the external conductor path which is
used to provide energy to electrical load 24.
The operation of the exemplary PEM fuel cell of FIG. 1 will now be
described in detail. Two electrochemical reactions are required for
the operation of the fuel cell--an anode reaction and a cathode
reaction. The anode reaction for a PEM cell may be written as:
H.sub.2.fwdarw.2H.sup.++2e.sup.-
The cathode reaction may be written as:
.times..times..times..times..fwdarw..times. ##EQU00001##
The overall reaction may then be written as:
.times..fwdarw..times. ##EQU00002##
Catalysts are generally required to facilitate the reactions. The
anode catalyst is typically nickel or platinum powder deposited in
a very thin layer on the porous anode. Flow channeling devices are
typically used to force the gaseous hydrogen to flow along a long,
serpentine path so that it remains in contact with the catalyst for
an extended period. The catalyst facilitates the splitting of the
diatomic hydrogen into free hydrogen nuclei (free protons) and free
electrons.
The proton exchange membrane is configured to allow the passage of
free protons (the hydrogen nuclei) but to prevent the passage of
the free electrons. Thus, the hydrogen nuclei pass through the PEM
but the free electrons cannot. Instead, the free electrons are
collected by negative charge collector 54 and forced to flow
through external conductor path 22. The free electrons pass through
positive charge collector 56 and ultimately to cathode 16.
At the cathode the free electrons combine with the oxygen and the
hydrogen nuclei passing through the PEM to form water. A catalyst
is generally used for the cathode reaction as well, with platinum
being a common example.
Many other components are included in actual PEM fuel cell designs.
These include:
(1) Channels for removing the water formed at the cathode;
(2) Devices for maintaining the appropriate conditions for the
PEM;
(3) Cooling devices for removing excess heat produced by the
electrochemical reactions; and
(4) Gas throttling valves for controlling the output of the fuel
cell.
FIG. 2 depicts a different type of fuel cell in which a solid oxide
is used for electrolyte 14. This type is often referred to as a
"SO" fuel cell. Most commonly a yttria-stabilized zirconia is used
as the electrolyte. SO fuel cells operate at relatively high
temperatures (800 to 1,000 degrees centigrade). The anode and
cathode reactions differ from the reactions existing in a PEM cell.
The anode reaction for an SO cell may be written as:
H.sub.2+O.sup.2-.fwdarw.H.sub.2O+2e.sup.-
The cathode reaction may be written as:
.times..times..times..fwdarw. ##EQU00003##
The overall reaction may again be written as:
.times..fwdarw..times. ##EQU00004##
The current vector in the device is the same as for the PEM cell,
but of course the ions move in the opposite direction. In the SO
fuel cell, an ionized oxygen atom moves from the cathode side of
the electrode toward the anode side. Thermal management and water
removal may also pose differing challenges. However, the conceptual
operation of PEM cell and the SO cell are grossly similar.
As those skilled in the art will know, the voltage produced by an
individual cell such as shown in FIG. 1 or 2 is quite
small--typically in the range of 0.7V. The electrical current
produced by each cell is a function of charge accumulation. Thus,
one may linearly increase the current produced by increasing the
surface area of the components. Larger anodes and cathodes produce
more current. The voltage, however, is fixed by the electrochemical
reactions themselves.
The low voltage produced by a single cell is not very useful,
particularly if it must be conveyed for any significant distance.
The solution to this problem is to "stack" multiple cells together
in the same way that single battery cells are stacked to increase
voltage. FIG. 3 provides a conceptual depiction of a "stacked"
arrangement of two SO fuel cells. Cell "A"--shown on the left--is
identical to the single cell shown in FIG. 2. Cell "B"--shown on
the right--is also identical.
However, the external electrical circuits have been reconfigured to
stack the voltage produced. The reader will observe that external
conductor path 22 has been connected from negative charge collector
54 on Cell A to positive charge collector 56 on Cell B. Linking
circuit 34 has been used to connect negative charge collector 54 on
Cell B to positive charge collector 56 on Cell A. As a result, free
electrons created by the anode reaction in Cell A are transported
by external conductor path 22 to the cathode reaction in Cell B
(where they react with diatomic oxygen to form oxygen atoms). Free
electrons formed by the anode reaction in Cell B are transported
via linking circuit 34 to the cathode reaction in Cell A.
Those skilled in the art will quickly realize that linking circuit
34 may be eliminated by simply pushing positive charge collector 56
of Cell A and negative charge collector 54 of Cell B together
(providing that the mating surfaces of the charge collectors are
suitably conductive). This is in fact what is done in most fuel
cell "stack" assemblies. FIG. 4 shows this configuration, with the
exception of separator plate 36 being substituted for a pair of
mating charge collector plates. Separator plate 36 is made of
conductive material. It must be able to survive exposure to the
charged gaseous oxygen environment on one side and the charged
gaseous hydrogen environment on the other.
Looking at the configuration of FIG. 4, the reader will realize
that the two cell stack shown could be expanded to three cells,
four cells, or any desired additional number. FIG. 5 shows a prior
art design using this approach in which six cells (A through F)
have been stacked in series. If each cell produces 0.7 volts, then
a stack of six such cells will (neglecting losses) produce 4.2
volts. Thus, a fuel cell designer using the prior art approach is
able to: (1) produce increasing current by increasing the surface
area of the components, and (2) produce increasing voltage by
increasing the number of individual fuel cells in the stack.
Additionally, the mechanical arrangement allows the entire assembly
to be held together using sets of tie rods that pass through the
assembly. The ends of the tie rods are threaded and nuts are
tightened on these threaded ends to clamp the stack together.
Suitable insulating and sealing components are of course added to
the tie rods so that the reactants don't leak and no electrical
short circuits are created.
The back-to-back stack approach does, however, have some recognized
shortcomings. These include, among others: (1) The separator plate
must be made of a material that can resist the oxidizing and
reducing environments, (2) The tightly packed nature causes heat
dissipation problems; (3) The tightly packed nature causes problems
with feeding in the reactant gases.
BRIEF SUMMARY OF THE PRESENT INVENTION
The present invention comprises a fuel cell assembly in which one
or more dual cell modules is created by "sandwiching" a first
reactant chamber between two electrolyte assemblies and enclosing
the result within a surrounding vessel containing the second
reactant. Each dual cell module thereby contains two operating
electrolyte assemblies. For example, a dual cell module may be
created by sandwiching a hydrogen diffusion layer between two solid
oxide electrolyte assemblies. The surrounding vessel would then be
flooded with oxygen.
In such a configuration it is not possible to physically stack
multiple cells together in order to create a series electrical
connection and thereby increase the voltage produced. Instead,
separate electrical conductors must be provided to create the
proper connections. In order to avoid the resistance losses
inherent in the use of edge connections, the present invention
preferably includes conductors that actually pass through the
electrolytes. These conductors are contained within an assembly
that electrically insulates the conductor where needed and provides
a gas-tight seal where needed. Each conductor assembly is referred
to as a "via."
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 is a schematic view, showing a prior art proton exchange
membrane fuel cell.
FIG. 2 is a schematic view, showing a prior art solid oxide
electrolyte fuel cell.
FIG. 3 is a schematic view, showing two prior art fuel cells
connected in series to increase the voltage.
FIG. 4 is a schematic view, showing two prior art fuel cells
connected in series using a separator plate.
FIG. 5 is a schematic view, showing a prior art stack of six fuel
cells.
FIG. 6 is a schematic view, showing a dual electrolyte fuel cell
made according to the present invention.
FIG. 7 is a schematic view, showing the creation of an electrical
circuit that is suitable for use with the fuel cell of FIG. 6.
FIG. 8 is a schematic view, showing the use of internal vias to
carry electrical current in the present invention.
FIG. 9 is an exploded perspective view, showing a simplified
depiction of the vias connected to an anode.
FIG. 10 is a detailed sectional view, showing the vias connected to
an anode and a cathode.
FIG. 11 is a detailed sectional view, showing the current flow
through the vias.
FIG. 12 is a schematic view, showing the vias being used to connect
two fuel cells made according to the present invention.
FIG. 13 is a schematic view showing the vias being used to connect
three fuel cells made according to the present invention.
FIG. 14 is a schematic view, showing a fuel cell made according to
the present invention in which the locations of the fuel and the
oxidizer have been reversed.
FIG. 15 is a perspective view with a cutaway, showing one possible
construction of a fuel cell made according to the present
invention.
TABLE-US-00001 REFERENCE NUMERALS IN THE DRAWINGS 10 fuel cell 12
anode 14 electrolyte 16 cathode 18 fuel inlet 70 oxygen inlet 22
external conductor path 24 electrical load 30 hydrogen diffusion
layer 32 oxygen diffusion layer 34 linking circuit 36 separator
plate 38 vessel 40 via 42 master anode 44 master cathode 46
conductor 48 insulator/seal 50 dual cell module 52 attachment 54
negative charge collector 56 positive charge collector
DETAILED DESCRIPTION OF THE INVENTION
The present invention includes a novel arrangement for the
components of a fuel cell, in which two electrolytes are connected
to a single reactant chamber. Internal electrical conduits
preferably carry the electricity produced from cell to cell so that
the voltage produced may be stacked in series without the need for
edge connections.
FIG. 6 shows a dual cell module constructed according to the
present invention. As for the prior art, separate chambers are used
for the fuel and oxidizer. The fuel and oxidizer chambers may be
reversed if desired. In the embodiment of FIG. 6, vessel 38 holds a
supply of gaseous oxygen fed in through oxygen inlet 20. Gaseous
hydrogen is fed into hydrogen diffusion layer 30 by hydrogen inlet
18.
A pair of electrolytes 14 flank hydrogen diffusion layer 30. The
diffusion layer is segregated from the surrounding vessel using
suitable walls (thereby forming a hydrogen manifold). The
particular embodiment shown is a solid oxide fuel cell. The term
"electrolyte assembly" means an assembly of an electrolyte and a
cathode on a first side of the electrolyte and an anode on the
second side of the electrolyte. The location of the anode and
cathode is determined by the reactant that is in the adjoining
chamber. For example, in the embodiment of FIG. 6, hydrogen is
placed in the diffusion layer 30. The example being a solid
oxide-type cell, the placement of the hydrogen means that anode 12
must lie between the hydrogen and electrolyte 14. The cathode 16
lies on the opposite side of the electrolyte. Hydrogen diffusion
layer 30 is sealed off from the surrounding oxygen inside vessel 38
but it is open to the two electrolyte assemblies.
Vessel 38 contains the second reactant diffusion layer. In the
embodiment shown, the second reactant diffusion layer contains
oxygen. The oxygen surrounds the first reactant diffusion layer
(hydrogen diffusion layer 30) and the two electrolyte
assemblies.
The electrolyte assembly at "A" includes anode 12 on the hydrogen
side and cathode 16 on the oxygen side of electrolyte 14.
Electrolyte assembly "B" likewise includes anode 12 on the hydrogen
side and cathode 16 on the oxygen side. The reader will thereby
discern that the assembly shown in FIG. 6 actually includes two
complete fuel cells. Unlike the prior art stacked designs, no
separator plate is required. The elimination of the separator plate
is considered advantageous since, in the prior art designs, the
separator plate must be both conductive and able to withstand the
oxidizing environment on one side and the reducing environment on
the other.
This assembly is referred to as a "dual cell module." It is the
basic building block of an operational fuel cell using the
inventive technology. In the prior art a first reactant chamber is
paired with a second reactive chamber with an electrolyte assembly
in between. In the present invention a first reactant chamber is
paired with a surrounding volume of a second reactant and two
electrolyte assemblies are present.
The reader will also discern, however, that the simple stacking
arrangement for assembling multiple cells in series (as in FIG. 4)
is not possible for the assembly of FIG. 6. The assembly of FIG. 6
includes two cells, but appropriate conductor paths must be
provided to "wire" them in series. FIG. 7 schematically depicts the
electrical connections needed to place the two cells in series.
External conductor path 22 in this example is connected between
cathode 16 of cell B (+) and anode 12 of Cell A (-). Linking
circuit 34 is connected between anode 12 of cell B(-) and cathode
16 (+) of cell A.
The operation of the assembly thus connected is as follows:
Diatomic gaseous oxygen is ionized at the cathode on each side of
the assembly. The ionized oxygen nuclei then flow inward, across
the two electrolytes 14. The oxygen nuclei combine with ionized
hydrogen nuclei at the two anodes 12 to form water and free
electrons. The free electrons formed at the anode in cell B are
carried by linking circuit 34 to the cathode at cell A, where they
react to form ionized oxygen. The free electrons formed at the
anode of cell A are carried by external conductor path 22 to the
cathode at cell B, where they also react to form ionized
oxygen.
Physical connections such as those depicted in FIG. 7 are "edge"
connections, meaning that a conduit is typically attached to an
exposed edge of the plate that is a cathode or anode. The use of
such edge connections creates an inherent limitation. As those
skilled in the art know, a fuel cell designer is often seeking to
meet specified voltage and current requirements for the complete
fuel cell assembly. Voltage may be increased by linking additional
cells together in series. Current is generally increased by
increasing the surface area of the electrolyte assembly--the anode,
cathode, and electrolyte itself (increasing the "plate size").
If the voltage produced by a given plate is only extracted at the
plate's edge, then a significant increase in plate size introduces
unacceptable internal resistance losses. A simple consideration of
two examples illustrates this point. A small fuel cell might use a
plate size of 10 centimeters by 10 centimeters. If the current
produced by the anode and cathode is extracted using a single
conductor along one entire edge of the anode or cathode, then the
maximum distance between a point of current creation and the point
of current extraction is 10 cm.
A larger fuel cell might use a plate size of 100 cm by 100 cm. The
maximum distance is then 100 cm. The resistance of a conductor is
generally proportional to its length. Thus, the resistance losses
for the longest run on the large fuel cell are 10 times greater
than for the longest run on the small fuel cell. Given the fact
that nominal voltage produced in a hydrogen/oxygen fuel cell is
only about 0.7 V, one may easily see that increasing the plate size
for a fuel cell rapidly reaches a problem with diminishing
returns.
A prior art solution to this problem has been assembling
series-connected stacks of "small" fuel cells in parallel to
increase the total current and reduce resistance losses within each
cell. While this solution does work, it requires an assembly of
considerable complexity. The present invention preferably avoids
this problem by eliminating the use of edge connections. Instead,
the present invention passes the electrical current through the
electrolytes themselves using one or more conductor assemblies
referred to as "vias." Each via preferably includes a conductor, an
insulating surrounding material, and one or more sealing components
designed to prevent the leakage of the reactants.
FIG. 8 schematically depicts this solution. Master anode 42 and
master cathode 44 are used to collect the charges. External
conductor path 22 passes from the master anode to the master
cathode. The master anode and master cathode are connected to the
fuel cell anodes and cathodes using the internal vias. Master anode
42 is electrically connected to anode 12 in cell A using one or
more vias 40. The vias connecting the master anode to the anode in
cell A pass through cathode 16 and electrolyte 14 in cell A.
However, these vias are electrically insulated from cathode 16 and
electrolyte 14. Further, the vias do not allow any significant
amount of gaseous oxygen or hydrogen to leak through the
electrolyte. They also provide a positive seal for the electrolyte
material itself (especially significant in cases where the
electrolyte includes a wetting agent).
One or more vias 40 electrically connect cathode 16 in cell A to
anode 12 in cell B. These vias pass through electrolyte 14 and
anode 12 in cell A. However, they are electrically insulated from
these components. They also provide a positive seal so that no
hydrogen gas leaks through the electrolyte along the vias.
Finally, one or more vias 40 electrically connect cathode 16 in
cell B to master cathode 44. In studying the circuit path created
by the vias in FIG. 8, those skilled in the art will readily
perceive that the two cells (A and B) have been stacked in series.
The circuit is equivalent to the connections shown in FIG. 7 (apart
from the use of "master" anodes and cathodes).
The use of the internal vias allows the creation of a "stacked"
fuel cell having lower internal resistance losses. FIG. 9 readily
illustrates this advantage. FIG. 9 shows how a plurality of vias
may be connected to a single anode 12. The exemplary vias are shown
in an exploded state. Each via includes a central conductor 46
attached to anode 12 by attachment 52. Insulator 48 slides over
conductor 46 and provides electrical insulation as well as the
necessary sealing function (separate sealing components may be used
as well).
Multiple vias may be distributed across the "face" of each anode or
cathode. Each via carries the current to or from an associated
region of the anode or cathode. The use of such vias reduces the
maximum distance that a particular charge must travel from its
point of creation to the conductor that carries it away.
FIGS. 10 and 11 illustrate this advantageous concept. FIG. 10 is a
detailed sectional elevation view. Its location in the assembly as
a whole is noted in FIG. 8. FIG. 10 includes three of the vias (one
connecting the anode of cell A to the master anode and two
connecting the cathode of cell A to the anode of cell B). The
reader will observe how each via 40 includes a central conductor 46
surrounded by an insulator/seal 48. The insulator/seal is
positioned to prevent any leakage of the reactants through
electrolyte 14. While the reactant-sealing aspect of insulator 48
is obviously significant, the electrical-insulating properties may
not be. There are no free electrons in the electrolyte of the fuel
cell. Thus, at least for the portions of the vias passing through
the electrolyte, it may not be necessary to provide electrical
insulation.
One approach could be to provide uninsulated vias through the
electrolyte. Contact pads could be placed in the anode and cathode
assemblies. These contact pads would make the electrical connection
with the exposed end of the via emerging from the electrolyte. Each
contact pad would need to be electrically insulated from the
balance of the anode or cathode, but this could be done using
suitable geometry.
FIG. 11 depicts the current flow through the three vias. In the
central via, the flow of electrons is from anode 12 and away (to
the left) toward the master anode. Those skilled in the art will
know that the current vector proceeds in the opposite direction of
the electron flow. Thus, the current vector shown for this via (I)
proceeds to the right. Electrical current proceeds from this via
into anode 12 and conceptually "spreads" through the anode plate as
depicted by the arrows. Conversely, electrical current flows from
the plate of cathode 16 and into the two vias leading away to the
right.
The use of internal vias allows many cells of the inventive design
to be stacked in series without experiencing the internal
resistance losses that would occur with edge connections. FIG. 12
shows an embodiment of the present invention in which four cells
are connected in series. A pair of hydrogen diffusion layer
manifolds are fed by a pair of hydrogen inlets 18. Surrounding
vessel 38 is again supplied with gaseous oxygen through oxygen
inlet 20. The four cells are of course an assembly of two "dual
cell modules" within a single vessel 38. The term "dual cell
module" is intended to encompass a single gas diffusion layer that
is "sandwiched" between a pair of electrolyte assemblies.
Master anode 42 is electrically connected by vias to anode 12 in
cell A. Cathode 16 in cell A is electrically connected by vias to
anode 12 in Cell B. Cathode 16 in cell B is electrically connected
by vias to anode 12 in cell C. Cathode 16 in cell C is electrically
connected by vias to anode 12 in cell D. Cathode 16 in cell D is
electrically connected by vias to master cathode 44. An external
electrical path is then created between master anode 42 and master
cathode 44 (including a load that is to be powered by the fuel
cell). In this arrangement, a series connection of four individual
fuel cells is created within a single vessel 38.
Of course, even more individual cells may be connected in series.
FIG. 13 shows an assembly in which 6 cells (A-F) are connected in
series within a single vessel 38. Within the practicalities of
mechanical packaging a much larger stack of cells may also be
created.
The prior exemplary embodiments have all used an oxidizer (diatomic
oxygen) in the surrounding container and a fuel (diatomic hydrogen)
in the gas diffusion layer within each dual cell module. Of course,
the inventive assembly can also be created with the reactants
reversed. FIG. 14 shows an embodiment in which gaseous oxygen is
fed into the gas diffusion layer within a dual cell module and
gaseous hydrogen is fed into the surrounding vessel 38. This
particular example is a solid oxide fuel cell. The reader will
note, of course, that the position of the anodes and cathodes have
been reversed in each electrolyte assembly.
The embodiment of FIG. 14 shows only one dual cell module. However,
there is no reason why two or more modules may not be configured in
this way, as was illustrated for the prior embodiments.
The embodiments disclosed have been represented in schematic form.
Those skilled in the art may tend to think of the electrolyte
assemblies as square plates and consequently think of the assembly
as a whole as being made of square plates (as is true for
conventional "stack" fuel cell assemblies). While one certainly can
make the components in a square shape, the invention is by no means
limited to such shapes.
FIG. 15 shows a cutaway view of an embodiment in which each dual
cell module 50 is constructed using a round cross section. In this
embodiment, the anode, cathode, electrolyte, and gas diffusion
layer are all made with a round cross section. An array of vias
connect the multiple dual cell modules 50 together in order to
electrically stack them in series. Vessel 38 surrounds the assembly
of dual cell modules. Oxygen inlet 20 feeds oxygen into the vessel.
A hydrogen manifold feeds gaseous hydrogen to multiple hydrogen
inlets 18, each of which feeds a particular dual cell module.
A master anode and master cathode is contained within vessel 38 in
this embodiment. Large electrical conductors pass through the walls
of the vessel to carry the electrical current to an external
load.
The configuration shown in FIG. 15 is not necessarily preferred,
and may in fact pose challenges for temperature management and
water removal. However, it does serve to demonstrate that the
invention can be made using a wide variety of geometric
configurations. Further, the embodiment of FIG. 15 shows a more
typical arrangement of vias 40 that would be used with an
electrolyte assembly having a relatively large surface area. The
use of many vias allows the current to be carried from module to
module without suffering significant resistance losses.
Many other embodiments are possible. Embodiments of the invention
may include one or more of the following features:
1. A group of vias passing through an individual dual cell module
may be gathered into a master cathode and master anode for each
module. The master cathodes and master anodes could then be linked
by large, low-resistance conductors:
2. Switching circuits could be used to add or subtract some of the
dual cell modules in a series stack in order to increase or
decrease the voltage produced by the assembly;
3. Cooling devices could be added, such as water circulation
jackets;
4. Current sensing devices could be added to monitor the output of
the fuel cell; and
5. Automated control systems could be added to regulate the
reactant flow in order to stabilize the assembly's output.
One of the significant features of the present invention is the
ability to test each individual dual cell module for proper
function before it is assembled into a larger stack. Referring to
FIG. 15, each of the dual cell modules 50 could be connected to
supplies of reactant gases and tested for leaks, electrical
production, water production, stabilized temperature, etc. In this
way manufacturing defects can be found and corrected before a
particular dual cell module is assembled into a larger unit.
Although the preceding description contains significant detail, it
should not be construed as limiting the scope of the invention but
rather as providing illustrations of the preferred embodiments of
the invention. One skilled in the art may easily devise variations
on the embodiments described. Thus, the scope of the invention
should be fixed by the claims rather than the examples given.
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